Golden oldies like Des O'Conner and Rod Stewart may be fathering offspring into old and middle age, but experts are warning men who delay fatherhood that 41 could be the age their fertility wanes dramatically.
Researchers say even a year can make a difference to a man's fertility, and that after 41, the odds are stacked against them.
The warning comes after scientists studied IVF patients where the man's sperm was used to fertilise an egg from a donor. The researchers were able to separate out the effect of the man's age from that of the woman's. The eggs used were all from young, healthy females, so they ascertained that any differences in pregnancy rate was down to the donated sperm.
The results showed fertility declined by up to seven per cent each year between the ages of 41 and 45 in men. After that, it accelerated even faster.
The average age of the men presenting with a partner for IVF was 41, whilst the average age of men whose attempts were unsuccessful was 45.
The chances of pregnancy fell from 60 per cent at the age of 41 to just 35 per cent for the 45-year-olds.
Researcher Paula Fettback, of the Huntington Medicina Reproductiva clinic in Brazil, told reporters: 'Men have a biological clock too. It is not the same as for women but they can't wait forever to have children. They have to think about having children, especially after 45.'
A second study backed up the warning when it was shown that fertility declined rapidly in male mice from just a year old – which is the equivalent to middle-age in humans.
The researchers, from the Colorado Center for Reproductive Medicine, said they believed there would be 'some parallel' with men. 'We found an abrupt reproductive deterioration in mid-life, equivalent to humans in their 40s.'
What do you think? Do you worry about your man's dwindling fertility or biological clock?